1. Field of the Invention
The present invention relates generally to the field of solar panels or arrays, and more specifically, solar arrays that can be stowed during launch in a relatively small volume, and easily deployed in space to a usable size while maintaining a high degree of stiffness.
2. Description of the Related Art
Solar arrays are used by satellites and other space vehicles to generate electricity, and thus provide a valuable and renewable source of power to operate electronics and motors carried by the vehicle. The capacity to produce power is directly related to the exposed surface area of the array, but large arrays are difficult and expensive to launch. It is thus common practice to use arrays that are stowed during launch in a relatively small volume, and then deployed generate a large power-producing surface area when a desired position in space is achieved.
Spacecraft deployable solar arrays often need to achieve a high degree of stiffness after being deployed, which tends to counter the objective of having a small stowed volume. Generally this is because a smaller stowed volume reduces space available for tall, stiff sections, or would mandate a greater number of joints, connections, hinges, etc., each of which would potentially impact negatively on the deployed stiffness of the array. Moreover, in attempting to create a smaller stowed volume, it sometimes becomes necessary to design and use mechanically complex hinges. As a general rule, however, hinge cost usually goes up with complexity, while reliability potentially goes down.
U.S. Pat. No. 5,833,176 to Rubin et al. describes a bowed solar array in which the array consists of several panels that are connected to each other through hinges. In the stowed position, the panels fold onto each other in an accordion fashion so that in the stowed position, the panels take up a smaller volume relative to the deployed position. A tensioning mechanism includes pulleys associated with respective panels, and cables inter-connecting the pulleys of the array. The bowed panels and tensioning mechanism are intended in part to increase deployed stiffness.
U.S. Pat. No. 6,091,016 to Kester describes a solar panel assembly which uses a plurality of panels that are stowed one on top of the other, and deployed in accordion fashion. The panels are connected to each other by parallel hinges, and in the deployed state, the panels are curved in a direction parallel to the panel edges to which the panels are attached, again with the intent of increasing deployed stiffness.
U.S. Pat. No. 5,296,044 to Harvel et al. describes a solar array that deploys from a folded, flat triangular form to a circular deployed shape. Solar cells of suitable size and shape are mounted on a plurality of gores. When stowed, a lead spar is rotated to reduce the apex angles between adjacent spars, so the gores fold along their mid-gore flexures.
U.S. Pat. No. 6,147,294 to Dailey et al. describes a D-wing deployable solar array in which the panels that make up the array stow flat and are deployed in a bowed xe2x80x9cDxe2x80x9d shaped configuration. The patent describes efforts to enhance rigidity through the use of greater inertia.
In general, deployable solar arrays are available in various forms, some of which recognize and address stowed volume and deployed stiffness as problems. These include, but are not limited to traditional flat-panel rigid arrays that deploy accordion style, rigid arrays reinforced with deployable structures, flexible arrays supported by deployable masts or other structures, and curved/strained arrays.
Compared to the present invention, traditional flat-panel rigid arrays of equivalent power and stiffness would require extremely thick panels that would increase stowed volume and mass. Rigid arrays with deployable structures are generally complex and not cost effective. They may also consume substantial stowed volume. Flexible arrays stow in a very small volume, but rely on a deployable mast or other structure for deployed support, which can be somewhat heavy and complex. Moreover, they tend to lack the requisite stiffness, and generally provide no power when stowed. Curved/strained arrays are a variant from traditional designs, but are limited by the amount of strain that cast be applied due to the brittle nature of high-efficiency single-crystal solar cells. Amorphous cells can accept high levels of strain to help attain a desired degree of stiffness, but amorphous cells lack the efficiency of single-crystal cells.
A continuing need exists for improved solar panel structures that have relatively high structural stiffness in the deployed state, while maintaining a good ratio between stowed and deployed Volume.
The present invention provides a relatively high degree of deployed stiffness, a relatively compact stowed volume, and a relatively simple deployment mechanism. The invention also provides a favorable ratio of deployed stiffness to stowed volume for a given power output with a relatively simple design that is cost effective to produce.
The invention includes a series of similar or identical stiff beams connected by similar or identical stiff hinges that support a series of similar or identical non-structural panels, which in a typical field of use, are populated with solar cells. The centers of the beams are offset by approximately one beam width (plus clearance) so that they nest inside each other when stowed. The panels are attached alternately on the top or bottom of the stiff beams so that the panels nest without interference.
The surface between the beams is joined by another set of panels attached to the surface opposite that which the outer panels are attached to. These center panels add additional rigidity and are optionally populated with solar cells, when used in that field of use.
The result of using nesting beams is an array that stows and deploys in an accordion fashion, which is capable of being deployed using conventional hinges and dampers of traditional design.
The invention provides improved ratios of stowed volume to deployed stiffness for a given power output. The design is also highly producible due to the use of a number of similar or identical panels, beams, and hinges. It is also scalable, in the sense that it can be sized to the requirements of a given application, to attain almost any stiffness requirement with an efficient and producible solution. Also, the present structure can provide power when stowed, unlike flexible arrays.